Optical fiber connectors are a critical part of essentially all optical fiber communication systems. For instance, such connectors are used to join segments of fiber into longer lengths, to connect fiber to active devices, such as radiation sources, detectors and repeaters, and to connect fiber to passive devices, such as switches, multiplexers, and attenuators. The principal function of an optical fiber connector is to hold the fiber end such that the fiber's core is axially aligned with an optical pathway of the mating structure. This way, light from the fiber is optically coupled to the optical pathway.
Of particular interest herein are “expanded beam” optical connectors. Such connectors are used traditionally in high vibration and/or dirty environments, where “physical contact” between the fiber and the light path of mating connector is problematic. Specifically, in dirty environments, particulates may become trapped between connectors during mating. Such debris has a profoundly detrimental effect on the optical transmission since the particles are relatively large compared to the optical path (e.g., 10 microns diameter in single mode) and are therefore likely to block at least a portion of the optical transmission. Furthermore, in high-vibration environments, optical connectors having ferrules in physical contact tend to experience scratching at their interface. This scratching diminishes the finish of the fiber end face, thereby increasing reflective loss and scattering.
To avoid problems of debris in the optical path and vibration, a connector has been developed which expands the optical beam and transmits it over an air gap between the connectors. By expanding the beam, its relative size increases with respect to the debris, making the beam less sensitive to the interference caused by the debris. Further, transmitting the beam over an air gap eliminates component-to-component wear, thereby increasing the connector's tolerance to vibration. Over the years, the expanded-beam connector has evolved into a ruggedized multi-fiber connector comprising an outer housing, which is configured to mechanically interengaged with the outer housing of a mating connector, typically through a screw connection. Contained within the outer housing are a number of inner assemblies or “terminus.”
An example of a terminus 400 is shown in FIGS. 4a and 4b. Each terminus 400 comprises a sleeve 401, a ferrule assembly 408 contained within the sleeve 401 and adapted to receive a fiber 402, and a ball lens 440 at a mating end of the sleeve 401 optically coupled to the fiber 402. The ball lens serves to expand and collimate light through (or near) the connector interface. When two expanded-beam connectors are mated as shown in FIG. 4b, the terminus 400 is mated with a similar connector 400′ such that there is an air gap 421 between the ball lens 440, 440′ of each terminus 400, 400′. Such a connector is disclosed, for example, in U.S. Pat. No. 7,775,725 (herein the “'725 patent”) incorporated by reference in its entirety.
As mentioned above, the beam is expanded and focused by virtue of a glass lens. In a multi-mode embodiment, shown in FIGS. 4(a) and (b), a spacer 480 is used to space the fiber end face a distance away from the lens surface at the focal point of the ball lens. For a single-mode expanded-beam connector 500 configuration, shown in FIGS. 5(a) and (b), a glass material is used to produce a ball lens that has a focal point 590 precisely on the lens surface 540a so that the fiber end face can be brought in direct physical contact with the lens and prevent an air gap and reduce back reflection. Thus, the glass lens used for a single-mode expanded beam application is different from a multi-mode lens and is typically more expensive.
Regardless of whether the lens is configured for use in a multi-mode or single-mode connector, it is the most expensive component in the connector system. For large production quantities, it is therefore desirable to find a less expensive lens option. The present invention fulfills this need among others.